Tensile Strength of Hot Isostatic Pressed Silicon Nitride and Effect of Specimen Dimension

Tensile and three-point bending tests were conducted on a hot isostatic pressed silicon nitride. To examine the size effect on the tensile strength, two kinds of different-sized round test specimens were prepared. A special chucking device utilizing a powder cushion between the specimen and the grip surface was used to promote good alignment with increasing load. The percentage of bending stress at the fracture was less than 5%. The mean tensile strengths of large and small specimens were 63% and 74% of the mean value obtained by the three-point bending test on the same material, respectively. The Weibull moduil determined by the large and small tensile specimens were smaller than that in the case of the three-point bending test. These results indicate that care should be taken in Weibull-statistics-based strength comparison for different-sized specimens and different loading conditions.